A Hong Kong court is hearing arguments about the sentence for pro-democracy media founder Jimmy Lai and his co-defendants in a landmark national security case.

Hong Kong pro-democracy newspaper Apple Daily has increased its print run more than fivefold to 500,000 copies as residents lined up to buy the paper in a show of support for beleaguered press freedoms, a day after police arrested five top editors and executives.

Hong Kong police have used a sweeping national security law to arrest five editors and executives of a pro-democracy newspaper on charges of colluding with foreign powers.